It is well known that certain so-called trace elements, i.e., those which are required for plant growth, but in small amounts, can be added to the soil for utilization by plants. Some can also be added as a treatment to the leaves by spraying - indicated in the published literature as a "foliar spray". A good way to apply these trace elements is in the chelated form, e.g., a chelate of ethylenediaminetetraacetic acid (EDTA) or of N-(2-hydroxyethyl)iminodiacetic acid (HEIDA).
The zinc chelate of the latter chelating agent, while providing a good source of zinc, is limited in its applicability because of its low solubility in water. Trace metals are frequently applied as foliar sprays in water solution, but because of its low solubility it is not economical to apply Zn-HEIDA in this manner.
Zinc when applied as a foliar spray is used in its more soluble form as the chelate of EDTA, but the Zn-HEIDA is less costly to prepare and it would be beneficial if a way could be found to improve the solubility of its zinc chelate.
A method has now been found by which the water solubility of the zinc chelate of N-(2-hydroxyethyl)iminodiacetic acid is improved. The water solubility has been increased from about 0.5% Zn to more than 6% Zn by employing the method of the present invention for preparing the chelate. The improvement in the method comprises using ammonia, or ammonium hydroxide, in the preparation.